1. Field of the Invention
The present invention relates to a battery module which is constituted by stacking a plurality of unit batteries, and more particularly, to a battery module in which the structure of a barrier interposed between unit batteries is improved.
2. Description of the Related Art
Generally, a rechargeable battery can be discharged and then charged, unlike a primary battery which is not intended to be charged.
A low capacity battery constructed with a packed battery cell is used for a portable small-sized electronic device such as a mobile phone, a laptop computer, and a camcorder. A high capacity battery constructed with tens of battery cells which are connected has been widely used as a motor driving power source of a hybrid electric vehicle (HEV).
The rechargeable battery is manufactured in various shapes. A representative rechargeable battery may be in the form of a can-type battery or a prismatic battery.
The high capacity rechargeable battery used to drive a motor of an apparatus requiring a large amount of power, such as an electric vehicle, is constructed by connecting a plurality of high output rechargeable batteries in series.
Hereinafter, for the convenience of description, the high output rechargeable battery is denoted as a unit battery, and the high capacity rechargeable battery constructed with a plurality of electrically connected unit batteries is denoted as a battery module.
Each of the unit batteries includes an electrode assembly having positive and negative electrodes with a separator interposed therebetween, a casing having a space wherein the electrode assembly is accommodated, and a cap assembly which is engaged with the casing so as to seal the casing.
A plurality of the unit batteries are stacked in order to constitute a battery module.
Conventionally, barriers are interposed between the stacked unit batteries, and the stacked unit batteries are pressed together with a proper tightening pressure by using end plates disposed outside the stacked unit batteries, thereby assembling a single battery module.
However, in the conventional structure, the tightening pressure of the end plates is not uniformly applied to the stacked unit batteries. More specifically, a unit battery disposed at the center of the stacked unit batteries does not receive a properly applied pressing force, whereas a unit battery contacting the end plate does receive a properly applied pressing force.
In addition, the conventional battery module has a problem in that the tightening pressure applied to the unit batteries becomes loosened and irregular as time goes on.
More specifically, during the use of the unit batteries, a swelling phenomenon occurs in that the battery casing is swollen by gas generated by a chemical reaction inside the battery. As described above, due to the swelling phenomenon, the battery becomes deformed, for example, the battery casing becomes swollen. In addition, deformation energy of the battery may press the barrier or the end plate which is used to fix the unit batteries in the battery module so as to cause deformation.
The deformation of the unit batteries and the barrier affects contact characteristics between the unit batteries and the barriers, so that the unit batteries and the barriers cannot properly contact each other. Accordingly, heat transfer from the unit battery to the barrier is not properly performed, so that heat dissipation efficiency decreases.
In addition, it is reported that output efficiency of batteries is improved when a battery module is assembled by applying a predetermined tightening pressure to unit batteries. However, in the conventional structure, the tightening pressure applied by the barrier changes or reduces as time goes on. Therefore, there is a problem in that efficiency of the battery decreases.